U.S. patent application number 10/935228 was filed with the patent office on 2005-03-10 for threading-dislocation-free nanoheteroepitaxy of ge on si using self-directed touch-down of ge through a thin sio2 layer.
Invention is credited to Han, Sang, Li, Qiming.
Application Number | 20050054180 10/935228 |
Document ID | / |
Family ID | 34228837 |
Filed Date | 2005-03-10 |
United States Patent
Application |
20050054180 |
Kind Code |
A1 |
Han, Sang ; et al. |
March 10, 2005 |
Threading-dislocation-free nanoheteroepitaxy of Ge on Si using
self-directed touch-down of Ge through a thin SiO2 layer
Abstract
A method of forming a virtually defect free lattice mismatched
nanoheteroepitaxial layer is disclosed. The method includes forming
an interface layer on a portion of a substrate. A plurality of seed
pads are then formed by self-directed touchdown by exposing the
interface layer to a material comprising a semiconductor material.
The plurality of seed pads, having an average width of about 1 nm
to 10 nm, are interspersed within the interface layer and contact
the substrate. An epitaxial layer is then formed by lateral growth
of the seed pads over the interface layer.
Inventors: |
Han, Sang; (Albuquerque,
NM) ; Li, Qiming; (Albuquerque, NM) |
Correspondence
Address: |
Min, Hsieh & Hack, LLP
c/o PortfolioIP
P.O. Box 52050
Minneapolis
MN
55402
US
|
Family ID: |
34228837 |
Appl. No.: |
10/935228 |
Filed: |
September 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60501274 |
Sep 9, 2003 |
|
|
|
Current U.S.
Class: |
438/479 ;
257/E21.129; 257/E21.131 |
Current CPC
Class: |
H01L 21/0245 20130101;
H01L 21/02521 20130101; H01L 21/02647 20130101; H01L 21/02642
20130101; H01L 21/02532 20130101; H01L 21/02381 20130101 |
Class at
Publication: |
438/479 |
International
Class: |
H01L 027/01 |
Goverment Interests
[0002] This invention was made with government support under Award
No. DMR-0094145 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
What is claimed is:
1. A method of forming a semiconductor layer comprising: forming an
interface layer on a portion of a substrate; exposing the interface
layer to a material comprising a semiconductor material to form a
plurality of seed pads interspersed within the interface layer and
contacting the substrate; and forming a semiconductor layer by
lateral growth of the seed pads over the interface layer.
2. The method of forming a semiconductor layer of claim 1, wherein
exposing the interface layer to a material comprising a
semiconductor material to form a plurality of seed pads through a
portion of the interface layer comprises heating at a temperature
between about 500.degree. C. and about 750.degree. C.
3. The method of forming a semiconductor layer of claim 1, wherein
exposing the interface layer to a material comprising a
semiconductor material to form a plurality of seed pads through a
portion of the interface layer uses molecular beam epitaxy.
4. The method of forming a semiconductor layer of claim 1, wherein
the interface layer has a thickness of about 1 .ANG. to about 30
.ANG..
5. The method of forming a semiconductor layer of claim 1, wherein
each of the plurality of seed pads has a width of about 2 nm to
about 8 nm.
6. The method of forming a semiconductor layer of claim 1, wherein
the semiconductor layer comprises a threading dislocation density
of about 1.times.10.sup.5 cm.sup.-2 or less.
7. The method of forming a semiconductor layer of claim 1, wherein
the substrate comprises silicon and the plurality of seed pads
comprise germanium.
8. The method of forming a semiconductor layer of claim 1, further
comprising forming a second semiconductor layer over the
semiconductor layer, wherein the second semiconductor layer
comprises at least one element from Group II, Group III, Group IV,
Group V, and Group VI.
9. The method of forming a semiconductor layer of claim 1, wherein
the interface layer comprises at least one of, SiO.sub.2,
Si.sub.3N.sub.4, siliconoxynitride, and anodized aluminum oxide
(AAO).
10. The method of forming a semiconductor layer of claim 1, wherein
the step of forming a semiconductor layer by lateral growth of the
seed pads over the interface layer forms a semiconductor layer
having a thickness greater than a critical thickness (h.sub.c).
11. A method of forming a semiconductor layer comprising: forming
an oxide layer on a portion of a semiconductor substrate; forming
by self-directed touchdown a plurality of seed pads comprising
germanium, wherein the plurality of seed pads are interspersed
within the oxide layer and contact the semiconductor substrate; and
forming a germanium layer by lateral growth of the seed pads over
the oxide layer.
12. The method of forming a semiconductor layer of claim 11,
wherein forming a germanium layer by lateral growth of the seed
pads over the oxide layer results in the semiconductor layer
comprises a threading dislocation density of less than
1.times.10.sup.5 cm.sup.-2.
13. The method of forming a semiconductor layer of claim 11,
wherein the plurality of seed pads are separated from each other by
about 1 nm to 15 nm.
14. The method of forming a semiconductor layer of claim 11,
wherein an average seed pad width is about 1 nm to 10 nm.
15. The method of forming a semiconductor layer of claim 11,
wherein the oxide layer is about 1 .ANG. to 30 .ANG. thick.
16. The method of forming a semiconductor layer of claim 11,
wherein the semiconductor substrate comprises silicon.
17. The method of forming a semiconductor layer of claim 11,
further comprising forming a second semiconductor layer over the
semiconductor layer.
18. The method of forming a semiconductor layer of claim 11,
wherein the step of forming a germanium layer by lateral growth of
the seed pads over the oxide layer forms a germanium layer having a
thickness greater than 2 nm.
19. A semiconductor device comprising: a substrate; an oxide layer
disposed on a portion of the substrate; a plurality of seed pads
formed by self-directed touchdown, wherein the plurality of seed
pads are separated from each other by the oxide layer; and a
semiconductor layer disposed over the substrate, wherein the
semiconductor layer is formed by lateral growth of the seed pads
over the oxide layer.
20. The semiconductor device of claim 19, wherein the seed pad
comprises germanium.
21. The semiconductor device of claim 19, wherein the oxide is
about 1 .ANG. to 30 .ANG. thick.
22. The semiconductor device of claim 19, wherein the semiconductor
layer comprises a threading dislocation density of less than
1.times.10.sup.5 cm.sup.-2.
23. The semiconductor device of claim 19, wherein the semiconductor
layer has a thickness greater than a critical thickness
(h.sub.c).
24. The semiconductor device of claim 19, further comprising a
second semiconductor layer over the semiconductor layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 60/501,274 filed on Sep. 9, 2003, the
disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to. semiconductor devices and
methods for their manufacture and, more particularly, relates to
epitaxial growth of lattice mismatched systems.
BACKGROUND OF THE INVENTION
[0004] Conventional semiconductor device fabrication is generally
based on growth of lattice-matched layers. A lattice mismatched
epitaxial layer at a semiconductor interface can lead to a high
density of dislocations that degrade semiconductor device
performance. Over the past several years, however, there has been
increased interest in epitaxial growth of lattice-mismatched
semiconducting material systems. Lattice mismatched systems can
provide a greater range of materials characteristics than silicon.
For example, the mechanical stress in a lattice mismatched layer
and control of its crystal symmetry can be used to modify the
energy-band structure to optimize performance of optoelectronic
devices. Lattice mismatched systems can also enable compound
semiconductor devices to be integrated directly with Si-based
complementary metal oxide semiconductor (CMOS) devices. This
capability to form multifunction chips will be important to the
development of future optical and electronic devices.
[0005] Problems arise, however, because an epitaxial layer of a
lattice-mismatched material on a substrate is often limited to a
critical thickness (h.sub.c), before misfit dislocations begin to
form in the expitaxial material. For example, h.sub.c=2 nm for a
germanium epitaxial layer on a silicon substrate. Because of the
relatively small h.sub.c and the large dislocation densities at
thicknesses greater than h.sub.c, use of the heteroepitaxial layer
is impractical.
[0006] Thus, there is a need to overcome these and other problems
of the prior art and to provide a method to grow defect free
heteroepitaxial layers of lattice mismatched systems.
SUMMARY OF THE INVENTION
[0007] According to various embodiments, the present teachings
include a method of forming a semiconductor layer including forming
an interface layer on a portion of a substrate. The interface layer
is exposed to a material comprising a semiconductor material to
form a plurality of seed pads interspersed within the interface
layer and contacting the substrate. A semiconductor layer is then
formed by lateral growth of the seed pads over the interface
layer.
[0008] According to various embodiments, the present teachings also
include a method of forming a semiconductor layer including forming
an oxide layer on a portion of a semiconductor substrate. A
plurality of seed pads comprising germanium are formed by
self-directed touchdown. The plurality of seed pads are
interspersed within the oxide layer and contact the semiconductor
substrate. A germanium layer is then formed by lateral growth of
the seed pads over the oxide layer.
[0009] According to various embodiments, the present teachings
further include a semiconductor device including a substrate and an
oxide layer disposed on a portion of the substrate. The
semiconductor device also includes a plurality of seed pads formed
by self-directed touchdown. The plurality of seed pads are
separated from each other by the oxide layer. The semiconductor
device further includes a semiconductor layer disposed over the
substrate, wherein the semiconductor layer is formed by lateral
growth of the seed pads over the oxide layer.
[0010] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
[0011] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate several
embodiments of the invention and together with the description,
serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 depicts a cross-section of a substrate in accordance
with exemplary embodiments of the invention.
[0013] FIG. 2 depicts a cross-sectional view of an interface layer
on a substrate in accordance with exemplary embodiments of the
invention.
[0014] FIG. 3A depicts a cross-sectional view of seed pad sites
interspersed in an interface layer in accordance with exemplary
embodiments of the invention.
[0015] FIG. 3B depicts a top-down view of seed pad sites
interspersed in an interface layer in accordance with exemplary
embodiments of the invention.
[0016] FIG. 4A depicts a cross-sectional view of seed pads on a
substrate and separated by portions of the interface layer in
accordance with exemplary embodiments of the invention.
[0017] FIG. 4B depicts a top-down view of seed pads on a substrate
and separated by portions of the interface layer in accordance with
exemplary embodiments of the invention.
[0018] FIG. 5 depicts a cross-sectional view of a semiconductor
layer formed by lateral growth of seed pads over portions of the
interface layer in accordance with exemplary embodiments of the
invention.
[0019] FIG. 6 depicts a cross-sectional view of a second
semiconductor layer on the semiconductor layer in accordance with
exemplary embodiments of the invention.
DESCRIPTION OF THE EMBODIMENTS
[0020] In the following description, reference is made to the
accompanying drawings that form a part thereof, and in which is
shown by way of illustration specific exemplary embodiments in
which the invention may be practiced. These embodiments are
described in sufficient detail to enable those skilled in the art
to practice the invention and it is to be understood that other
embodiments may be utilized and that changes may be made without
departing from the scope of the invention. The following
description is, therefore, not to be taken in a limited sense.
[0021] As used herein, the term "self-directed touchdown" refers to
a nucleation and growth process that is initiated without reliance
on an photolithographic mask to pattern a substrate or other
layer.
[0022] As used herein, the term "nanoheteroepitaxy" refers to
engineering a heterojunction at the nanoscale to relieve lattice
strain.
[0023] FIGS. 1 to 6 depict exemplary semiconductor devices with
nanoheteroepitaxal layers and manufacturing methods to form
semiconductor devices with nanoheteroepitaxal layers having a
lattice mismatched substrate and semiconductor layer in accordance
with various embodiments of the invention. The semiconductor
devices comprise a plurality of seed pads formed by self-directed
touch-down through a portion of an interface layer and on a
substrate. A semiconductor layer can then be formed by coalescence
of the seed pads over the portions of the interface layer. The
semiconductor layers formed by the exemplary methods have a
sufficiently low threading-dislocation density, regardless of the
critical thickness of the semiconductor layer, so that the
deposited semiconductor layer can be effectively used for
integrated circuit applications. For ease of illustration, the
invention will be described with reference to a manufacturing
process for formation of an epitaxial layer of germanium (Ge),
having a lattice parameter of about 5.66 .ANG., on silicon (Si),
having a lattice parameter of about 5.44 .ANG..
[0024] Referring to FIG. 1, a substrate 10 is shown. Substrate 10
can be, for example, a silicon substrate. Other substrate materials
can include any semiconductor material having a lattice-mismatch to
a desired epitaxial layer. The terms "lattice-mismatch" and
"lattice-mismatched material" as used herein refer to any materials
whose lattice parameters in a given crystalline plane or direction
are not identical. Lattice-mismatched materials can include, but
are not limited to, silicon and germanium, silicon and carbon,
silicon and GaAs, silicon and InP, and silicon and gallium
nitride.
[0025] As shown in FIG. 2, an interface layer 20 can be formed on
substrate 10. Interface layer 20 can be, for example, an oxide
layer, such as, a SiO.sub.2 layer, having a thickness of about 1
.ANG. to about 30 .ANG.. The SiO.sub.2 layer can be formed by
methods known in the art, such as, treating substrate 10 in a
Piranha solution or by thermal growth. Other interface materials
can include, but are not limited to, silicon nitride,
siliconoxynitride, anodized aluminum oxide (AAO), and other oxides.
In various embodiments, interface layer 20 can comprise an
amorphous material.
[0026] In various embodiments, properties of interface layer 20,
such as surface roughness and thickness, can be controlled to
tailor the defect morphology of the epitaxial layer. For example,
interface layer 20 can be formed using H.sub.2O.sub.2 to achieve a
monolayer of atomically flat SiO.sub.2 on a hydrogenated Si(100)
substrate.
[0027] After forming interface layer 20 on substrate 10, interface
layer 20 can be exposed to a material comprising a semiconductor
material. Exposure temperatures can be about 500.degree. C. to
about 750.degree. C. The semiconductor material can comprise, for
example, Ge. In various embodiments, molecular beam epitaxy can be
used to expose interface layer 20 to Ge. As shown in FIGS. 3A and
3B, the Ge can react with interface layer 20, to form interface
layer free areas 30, exposing portions of substrate 10. Interface
layer free areas 30 can form, for example, through reaction of the
Ge with the oxide film as follows:
SiO2(s)+Ge(ad).fwdarw.SiO(g)+GeO(g). Interface layer free areas 30
can be randomly distributed to form a remaining portion of
interface layer 25, and can be about 2 nm to about 8 nm wide. The
spacing between interface layer free areas can be about 2 nm to
about 14 nm.
[0028] As exposure to Ge by molecular beam epitaxy continues, Ge
can deposit in interface layer free areas 30. There is generally no
deposition on remaining portions of interface layer 25, due to
selective deposition. This self-directed touch-down of Ge on Si
occurs without lithography to pattern the substrate or interface
layer. The regions of Ge growth on Si substrate 10 can form
crystalline Ge islands, referred to herein as seed pads 40, shown
in FIGS. 4A and 4B. Seed pads 40 can then laterally overgrow and
coalesce, as exposure to Ge continues. As lateral growth of Ge seed
pads 40 over remaining SiO.sub.2 oxide layer 25 continues, Ge seed
pads 40 coalesce into a single semiconductor layer. The
semiconductor layer can be a virtually defect free single
crystalline epitaxial lateral overgrowth (ELO) layer.
[0029] FIG. 5 shows a semiconductor layer 50 formed by coalesced
seed pads having an atomically abrupt interface with substrate 10.
Semiconductor layer 50 can be virtually defect-free having a
threading dislocation density of about 1.times.10.sup.5 cm.sup.-2
or less. Stacking faults can exist over the remaining oxide layer
patches 25, but generally terminate within about 80 nm from the
SiO.sub.2-Ge interface. The thickness of semiconductor layer 50 can
be greater than the critical thickness h.sub.c, for example,
greater than the critical thickness of 2 nm for 100% Ge on Si. Seed
pads 40 can have an average width of about 1 nm to 10 nm. The
distance between seed pads can be about 3 nm or more.
[0030] In various embodiments, a second semiconductor layer 60 can
be deposited over the semiconductor layer. The second semiconductor
layer can comprise one or more materials from Group II, Group III,
Group IV, Group V, and Group VI, such as, for example, GaN, GaAs,
AlGaAs, InGaP, AlInP, AlInGaP, InGaAsN, SiGe. As shown in FIG. 6,
second semiconductor layer 60 can be formed on semiconductor layer
50.
[0031] A specific example of nanoheteroepitaxy to grow virtually
dislocation-free lattice mismatched materials will now be provided.
It is to be understood that the disclosed examples are exemplary
and in no way are intended to limit the scope of the invention.
EXAMPLE 1
[0032] Samples I was undoped Si(100) including an interface layer
of SiO.sub.2. Sample II was undoped Si(100) stripped of an
interface layer by exposure to HF.
[0033] Both sample substrates were first treated to remove
contaminates by immersion in a Piranha solution for about 5 minutes
to form a thin layer of SiO.sub.2 on the substrate. The Piranha
solution was prepared by mixing 4 volumetric parts of 2M
H.sub.2SO.sub.4 with 1 volumetric part of 30 wt % H.sub.2O.sub.2.
The samples were then treated for 5 minutes in an HF solution to
remove the SiO.sub.2 layer. The HF solution was prepared by
diluting a 49 wt % electronics grade HF solution to 11 wt % by
deionized H.sub.2O. The Piranha-HF treatments were repeated three
times.
[0034] A fresh Piranha solution was prepared and Sample I was
treated at 80.degree. for 10 minutes to form a thin layer of
chemical oxide. After treatment, Sample I was rinsed with deionized
H.sub.2O, and blow-dried with N.sub.2. No chemical oxide layer was
formed on Sample II.
[0035] Sample I was then immediately loaded into an ultrahigh
vacuum molecular beam epitaxy (UHV-MBE) chamber having a base
pressure of 4.times.10.sup.-10 Torr. Sample II was immediately
loaded into the UHV-MBE chamber after the third HF treatment that
removed the oxide layer. Both of the samples were heated to
620.degree. C. and a Knudsen effusion cell was used to expose the
samples to Ge. The effusion cell was operated at 1200.degree. C.
for a Ge growth rate of 100 nm/hour. During growth of Ge, the
chamber pressure was below 1.times.10.sup.-9 Torr.
[0036] Cross sectional transmission electron microscopy (XTEM)
showed that, in Sample I, amorphous oxide regions were interspersed
with Ge seed pads. A single crystalline Ge ELO layer, approximately
4 .mu.m thick, covered the amorphous oxide regions and seed pads.
The thickness of the oxide layer regions in Sample I was determined
to be 1.2 nm. The average dimension of the seed pads was about 7
nm, and the spacing between the seed pads ranged from 4 nm to 12
nm.
[0037] XTEM further showed that the Ge layer of Sample II, having
no seed pads, contained a network of dislocation segments primarily
within 250 nm from the Ge-Si interface. In contrast, the Ge ELO
layer of Sample I was free of a dislocation network. Only stacking
faults emanating from the seed pad-Ge interface existed along the
{111} planes in the Ge ELO layer of Sample I. Those stacking faults
terminated within 80 nm of the interface. As a result, Sample I,
fabricated with the oxide layer that resulted in seed pads, formed
an atomically abrupt Ge-Si interface and a virtually defect free Ge
ELO layer. Sample I had a threading dislocation density of about
1.times.10.sup.5 cm.sup.-2 or less. Sample II, however, formed
without the oxide layer and seed pads, formed a Ge layer containing
a network of dislocation segments.
[0038] Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with a
true scope and spirit of the invention being indicated by the
following claims.
* * * * *